tach problem

[Oregon260z]

I cant seem to get my tach on my 74 260z to work I got all the lights to work but the tach does nothing.. I have changed it out with 4 others and still nothing. Can someone please tell me how to make this *%@#*^ thing work. Where do the wires go to make the tach opperate? any help would be great. I have tried to look at wiring diagram but I cant see it well enough to trace the problem out. Also maybe a diagram showing how the coil and dizzy and everthing is spose to be hooked up showing positive and negetive the PO cut wires and taped wires so Iam unsure how the correct wires hookups.

Thanks

Jonathan

[Oregon260z]

wow no help or even input kool : (

[d240zx2]

There have been 47 views. If anyone knew the answer to your problem, wouldn't you assume they'd answer?? Could be no one knows the answer given the facts you presented. I know I don't.

[Walter Moore]

Sorry, I am not that familiar with the 260Z. On the 240 the power for the ignition goes through the tach (sort of) and that is how it senses the engine speed. The 260 must be similar.

I wonder if a previous owner jumpered around a bad tach to get the ignition to work...

[74L28Z]

Jonathan, maybe this diagram will help you better. It is from my 260Z shop manual. What were the other 4 tach's from? Reason I ask is that I went through three 260z tachs and were all bad and ended up using a 75-76 280Z tach and have no problems. I've heard the early tachs weren't as reliable as the later 280 versions.

Regards,

Lee

[alhbln]

The chart from 74L28Z is the right one. The 260 has a kickback driven tach (three wire tach), where one wire of the tach goes to the coil's negative terminal. Previous tachs for the 240Z were current driven tachs (four wire tachs) where the coil current is routed through a wire loop at the back of the tach.

From the wiring i would assume that the color of the tacho's wire going to the negative coil terminal is black. The wire coming out of the tach going to the dashboard wiring connector is yellow. You might want to do a continuity check with a multimeter from the three terminal dashboard wiring connector to the wires at your coil to make sure the wire is ok and you got the right one.

Do you have the factory ignition or a modified system? Can you post a photo showing your coil wiring?

Both the four wire as well as the three wire tach can be repaired in most cases, after a repair and calibration they are still quite good and not as unreliable as one may think. My '72 tach is quite on the point with a maximum error rate of 4% after calibration.

[ChrisZ]

I also like to add, thet there is a inline resistor in the tach wiring, maybe that one is blown.

My -73 also have the same kind of tach, it didn't work when i first got the car, i found out the wire was cut, when one PO installed a Pretronix, maybe it's worth a try to open up your harness to see if there is any bugs there.

Chris

[Oregon260z]

alhbln, I dont see a yellow wire or black ? The ignition is all stock I belive Iam not sure. Here are pics of the wires on the tach and the coil. The coil on + side goes to some negetive side of a block of some kind that has 2 other wires hooked to it. Then one the negetive side there is a wire going to my distributor and thats it no other wires.

Edited May 7, 2010 by Oregon260z

[zKars]

The wiring colors on the tach itself do not correspond to the wiring colours on the harness and on the diagram. On your tach picture , the Red/Black wire is the L (blue) wire in the wiring diagram. The green is the +12 line , the black is ground, I mean the two that connect to the white plastic terminal block on the tach.

Connect the tach back to the wiring harness. Check continuity from the Red/Black wire on the back of the tach to the - neg side of the coil. If they are not connected, then find that resistor that the wire passes through. It is on the passenger side foot well up in behind the glove box near where the fat bundle of wires goes through into the engine bay. It has blue tape around a black rubber rectangle cube about the size of the end of your thumb. It is a 2200 ohm resistor inside. Blue wire coming and going from it.

Also check that you +12v at the green wire on the back of the tach with the key on. Also confirm you have continuity between the black wire and the metal chassis anywhere on the car (ground).

Gets those checks done and get back to us.

Jim

[ChrisZ]

For the fun of it, you could also try to wire one of your spare tach's up per Jim's decribtion, direct to the battery and coil, it might bounce around a bit, being there is no resistor.

Chris

Edit, IIRC the tach wire is spliced in to the negative wire going from the dizzy to the coil,

Edited May 7, 2010 by ChrisZ

[Oregon260z]

Thanks everyone for the help found the problem the red/black wire was broke in harness so ran new wire tach works now.

Thanks again

Jonathan

[ChrisZ]

Good to here you got it fixed, i could use the guts from one of your spare tach's, ned to be working.

Let me know.

Chris